To clarify Peter's statement, "a fewer" is never correct. The reason for this is that the pronoun/adjective "few" means a small (or, in the case of "fewer," a smaller) number [of things, choices, nutrients, people, etc.] but always a number greater than one. In other words, "fewer" can only be used with plural nouns, hence the article "a" should not be used with it. In your case, because you would not write "People have a choices" (instead of "People have choices") or "consume a types of nutrients" ("consume types") you should not write "People have a fewer choices" or "a fewer types."